US3554873A - Simplified extractive distillation process for obtaining aromatics of differing boiling-point ranges - Google Patents

Simplified extractive distillation process for obtaining aromatics of differing boiling-point ranges Download PDF

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US3554873A
US3554873A US674682A US3554873DA US3554873A US 3554873 A US3554873 A US 3554873A US 674682 A US674682 A US 674682A US 3554873D A US3554873D A US 3554873DA US 3554873 A US3554873 A US 3554873A
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aromatics
column
extractive
extraction agent
distillation
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Gunter Luther
Jurgen Ludwig
Martin Schulze
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
    • B01D3/40—Extractive distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/04—Purification; Separation; Use of additives by distillation
    • C07C7/05—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds
    • C07C7/08—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds by extractive distillation

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  • the extractive distillation unfortunately has two short comings as against the liquid-liquid extraction. In the first place, there is a comparatively high portion of extraction liquid in the rafiinate phase of the extractive distillation plant. In the second place, the problem of obtaining products with widely difiering boiling-point ranges from the extractive distillation process is difficult to solve.
  • the extractive distillation method has therefore been used heretofore only for feed products with a content of non-aromatics up to about 20%, since in these cases the mentioned shortcomings were without significance, or otherwise the extractive distillation Was carried out in combination with a liquid-liquid distillation.
  • the non-aromatics containing mass drawn off from the extraction columns may be subjected to further treatment in separate auxiliary columns where any residues of lower boiling-point aromatics that may still be present are removed from the product, whereupon the bottom product of the auxiliary columns which substantially no longer contains any aromatics may be subjected to another extractive distillation.
  • this is done by collecting the different masses of non-aromatics products from the several extractive distillation columns and subjecting them to another common extractive distillation.
  • the final refining may also be effected in a normal distillation step.
  • the improvement consists in passing the mass to be processed after it comes from the extractive distillation column or columns through a plurality of in-series connected column systems, the number of said systems corresponding to the number of aromatics to be obtained, and subjecting the mass in each of said column systems successively to an extractive distillation and to a normal distillation and recovering from each system the desired aromatic fraction.
  • FIG. 1 illustrates, in a diagrammatic form, one single column system for use in the process of the invention
  • FIG. 2 illustrates a modified form of such column system
  • FIG. 3 is a flow sheet illustration of the extractive distillation process and apparatus of the invention. Secondary parts of apparatus such as evaporators, cooling-apparatus, heat exchangers, pumps and valves are omitted in the flow sheet to give a clear picture of the process.
  • the method of the invention accordingly differs from that of the mentioned copending application in that further separation of the extraction product mixture enriched by the preceding extractive-distillations, into individual fractions, takes place with the aid of a column system whose column sections not only perform the function of extractive-distillation but also the function of normal distillation.
  • a column system whose column sections not only perform the function of extractive-distillation but also the function of normal distillation.
  • a lower boiling aromatic component such as benzene
  • a refined (non-aromatics) product having a boiling point Within the range of the next higher boiling aromatic component, such as toluene.
  • This top product of the extractive-distillation is subsequently split, by distilling, into benzene and the nonaromatics of the toluene boiling range.
  • the concept of the column system used in the method r of the invention is best explained by reference to FIG. 1.
  • the column system shown therein consists of the four column sections 1a, 1b, 1c and 1d respectively.
  • the column sections 1a and 1b both primarily operate in the mode of extractive distillation, section 1a being an extractive stripper section and section 1b being an extractive rectifying section.
  • the column sections 10 and 1d both operate in the mode of normal distillation, section 10 being a distillative stripper section.
  • the extractive column sections 1a and 1b are interconnected by the product streams 4 and 5 in the same way as in a normal extractive-distillation column, both on the vapor side as well as on the liquid side.
  • the distillative column sections 10 and 1d are interconnected by the product streams 6 and 7 as in normal distillation, on the vapor side as well as on the liquid side.
  • the extractive column consisting of sections 1a and 1b, is connected at its head by the product stream 8 to the distillative column consisting of sections 10 and 1d.
  • This product stream 8 which may be vapor or liquid, is fed to the uppermost plate of the distillative stripper section Id.
  • extraction agent is supplied through a pipeline 2 to the uppermost plate of the extractive rectifying section 1b, a feed mixture obtained from the bottom of a preceding column being supplied through a pipeline 3 to the uppermost plate of the extractive stripper section 1a, whilst a reflux is supplied through a pipeline 12 to the uppermost plate of the distillative rectifying section 10.
  • the extraction product (e.g. aromatic) fraction to be obtained from such system is tapped off through pipeline 9, whilst the refined product (e.g. non-aromatic) fraction, having the boiling range of the extraction product fraction of the next column system, is tapped off through pipeline 10.
  • the refined product e.g. non-aromatic
  • the bottom of the extractive stripper section 1a consisting substantially of extraction agent and residual aromatics is tapped off through pipeline 11. Where appropriate, this bottom product may be supplied to a subsequent column system for further processing.
  • the column system shown in FIG. 1 may take various forms; the individual column sections may, for instance, be arranged as illustrated in FIG. 2, in which the reference numerals have the same significance as in FIG. 1.
  • the embodiment illustrated in FIG. 2 differs from that of FIG. 1 in that the extractive rectifying section 1b and the distillative rectifying section 10 are both constructed as parts of a single column unit also including the extractive stripper section 1a. Other form's are also possible.
  • this can be accomplished by allowing to remain in the extraction agent those extraction product-like substances (e.g. aromatics) originating from the feedstock which are not to be extracted or are to be only partially extracted. It is of course also possible to add to the extraction agent other extratcion product-like substances (aromatics) not to be extracted and not present in the feedstock. For example, it is possible to add toluene to the extraction agent if benzene and xylene are to be obtained by extractive-distillation of a feedstock containing these aromatics mixed with parafiins.
  • extraction product-like substances e.g. aromatics
  • aromatics extratcion product-like substances
  • the amount of extraction product-like substances (e.g. aromatics) to be added to the extraction agent may be up to 20% by volume referred to the extraction agent.
  • the amount of such an additive also depends on the pressure at which extractivedistillation is performed. This is subject to the rule that under condtions of elevated pressure (positive pressure) the amount of additive may be correspondingly reduced.
  • the extractive rectifying section 1b may be omitted if a yield of the next higher boiling extraction product (e.g. aromatic) fraction is not required. Moreover, it is possible to dispense with the distillative stripper section 1d if a yield and purification of the heads products of this column system (aromatic) are not required. Finally, an additional column section may be mounted upon the head of the extractive rectifying section 1b, the head of the aforementioned column section being fed with ex traction product-like substances (e.g. aromatics) or a fraction containing such substances and 'which serves for the additional extraction agent recovery.
  • ex traction product-like substances e.g. aromatics
  • the method of the invention may further include the step of returning to the extractive-distillation system a bottom product obtained from the last extractive stripper section and which consists of extraction agent feed of the required extraction products e.g. aromatics.
  • the sensible heat of this bottom product as well as of the bottom product of the extractive-distillation columns operated at higher pressures may then be employed for heating the extractive-distillation columns operated at lower pressures and/ or the distillative stripper sections.
  • the method according to the invention is not confined to the use of a particular extraction agent, the criterion for suitability being an adequate selectivity for separating the extraction products from the refined products.
  • the following substances are suitable extraction agents for separating aromatics from paraffins: propylene carbonate, N-oxyalkyl derivatives for 1,3-propane diamine and N-substituted morpholine. This enumeration does not, however, represent any limitation to the aforementioned compounds. Many other compounds may also be employed as extraction agents.
  • the method of the invention can be employed for the separation of any desired kinds of substances with any desired extraction agents if the attainably purity of the heads product of extractive-distillation is limited by a miscibility gap.
  • FIG. 3 this illustrates in block diagram-flowsheet form the principal plant components used, typically, to carry out the method of the invention for separating aromatics from paraflins: in this figure, all auxiliary devices which are of a lower order of significance for the method, such as heaters, coolers, heat exchangers, pumps, valves and the like, have 'been omitted in the interest of clarity.
  • the process will be described in relation to its use for refining a feedback consisting of a hydrocarbon mixture having the following composition by weight (in. kg.):
  • the weight ratio of extraction agent to feedstock should be equal to 3, that is 3000 kg. of extraction agent are employed.
  • the extraction agent consists of approximately 2880 kg. propylene carbonate and approximately 120 kg. toluene. Approximately 80% of this quantity of toluene is fed through a line 41 to the head of a first extractive-distillation column 14 and the remaining 20% is fed through a line 42 to the head of a second extractivedistillation column 19.
  • the toluene employed in the extraction medium may at least partly originate in the feedstock being extracted therefrom in the process as will be described and fed by recycle line 32 to the pipelines 41 and 42 from the toluene Output line 31.
  • the feedstock is introduced through a line 13 to a middle plate of the first extractive-distillation column 14 which operates at a pressure of approximately 3.5 atm.
  • the appropriate amount of the propylene carbonate constituent of the extraction agent is fed through a line 15 to one of the upper plates of the column 14.
  • a large proportion of the non-aromatics in the feed mixture escapes in vapour form through a line 16 at the head of the column and is fed into a manifold line 17.
  • the bottom product of the column 14 which contains the aromatics and the extraction agent in addition to the residue of nonaromatics passes through a line 18 to constitute the feed for the second extractive-distillation column 19 which operates at normal (atmospheric) pressure.
  • the feed in this case is also introduced to one of the middle plates of the column 19.
  • Propylene carbonate is fed through the line 20 to one of the upper plates of the column 19.
  • the non-aromatics escape in vapour form through a line 21 at the head of the column and, after condensation, are also fed into the manifold line 17.
  • the bottoms product of the column 19 is conveyed through a line 22 into a first column system 23 of the form illustrated in FIG. 2 sections 23a, 23b and 230 corresponding with sections 1a, 1b and 1c of FIG. 2 and being combined in a single column.
  • the side column 23d of the system 23 is a distillative stripper section corresponding with section 1d in FIG. 2.
  • the line 22 feeds between the extractive rectifying section 23b and the extractive stripper section 23a of that system, which system serves for the stripping of benzene from the said bottom product, benzene being discharged via a line 24.
  • Propylene carbonate is fed through a line 25 to the uppermost plate of the extractive rectifying section 23b.
  • a fraction containing the non-aromatics is drawn off from the bottom of the distillative rectifying section 23c and passes through a line 26 into the side column 23d, from which the non-aromatics are removed at the bottom and are fed into the manifold line 17 through a line 27.
  • the bottoms product of the extracting stripper section 23a which contains residual aromatics in addition to the extraction medium, is pumped through a line 28 into a second column system 29, again arranged as described with reference to FIG. 2, which serves the purpose of stripping the toluene from said bottom product.
  • Propylene carbonate is supplied through a line 30.
  • the extracted toluene is drawn off through a toluene output line 31, some being recycled, as described, to the extractive distillation columns 14 and 19 through the recycle line 32.
  • the side column 29d serves as distillative stripper section and is connected to the bottom of section 29c by a line 33.
  • the non-aromatics are drawn off through a line 34 which extends into the manifold line 17
  • the bottoms product of the column system 29, containing the xylene as well as the higher boiling aromatics and extraction agent is finally pumped through a line 35 into the final column system 36 which serves for extracting the xylene.
  • the column system 36 is again arranged as described in relation to FIG. 2 but differs in that, since the yield and purity of the C aromatics to be obtained by extraction of xylene from the bottom product of the column system 29 is immaterial, the system 36 does not include an extractive rectifying section, nor does it have an extraction agent feed.
  • the xylene is drawn off through a line 37.
  • the side column 36d functions as distillative stripper section and is connected to the bottom of the column section 36c via a line 38.
  • the remaining non-aromatics and the residual aromatics with a higher boiling point than xylene are withdrawn via a line 39 and fed to the manifold line 17.
  • the recovered extraction agent from the bottom of section 36a (predominantly propylene carbonate since toluene has been stripped therefrom by the column system 29) is delivered for reuse via the line 15 and the branch lines 20, 25, 30.
  • Fresh propylene carbonate is supplied through a line 40 when necessary to make good losses and to introduce this constituent of the extraction agent into the process when the plant is started up.
  • the higher boiling aromatics for example C aromatics
  • C aromatics it may be desirable for the higher boiling aromatics, for example C aromatics, to be extracted in addition to benzene, toluene and xylene. If these aromatics are required to be extracted from the mixture obtained from the bottom of the column section 36d, such mixture may be processed in a further column system. If no quantitative separation of the C aromatics is envisaged, such processing may be accomplished in a simple stripper column.
  • the feed stock after having been freed in extractivedistillation columns 14 and 19 of a large portion of the non-aromatic constituents, is withdrawn through conduit 22 and introduced into the first column system 23, for stripping off of benzene.
  • the product introduced into column system 23 has the following composition:
  • toluene content it has to be considered that in addition to the toluene content of the feed stock (150 kg.) also about 120 kg. toluene had been introduced into the system with the extraction agent.
  • the benzene which has been stripped off in column system 23, is withdrawn through conduit 24, and has the following composition:
  • the benzene is of a purity of 99.95%.
  • Non-aromatics 109.032 Benzene 1.943 Toluene 19.932
  • This fraction has the following composition:
  • Extractive distillation process for simultaneously obtaining different aromatics with different boiling point ranges from a feed stock containing varied amounts of non-aromatics along with the desired aromatics comprising passing the feed stock through at least one extractive distillation column while contacting it in said column with an at least partially non-aromatic selectively active extraction agent containing aromatics other than the aromatics to be recovered; withdrawing a liquid extract of aromatics and extraction agent from the bottom of said column while withdrawing the non-aromatics in vapor form at the top of said column; then passing said liquid extract of aromatics and extraction agent through a plurality of column systems arranged in series, one of said systems being provided for each desired type of aromatic; subjecting said liquid extract of aromatics and extraction agent in each of said systems to an extractive distillation followed by a conventional distillation, and withdrawing the aromatic to be recovered from the respective rectifying distillation, and also withdrawing non-aromatic from said stripping distillation.
  • An extractive distillation apparatus comprising at least two extractive distillation columns arranged in series and having connected to the last extractive distillation column a plurality of column systems arranged in series, at least one of said column systems being comprised of an extractive stripper section, an extractive rectifying section superposed on said extractive stripper section, and a distillative rectifying section superposed on said extractive rectifying section, and, connected with said distillative rectifying section, a separate distillative stripper section, means for introducing the mixture of extraction agent, aromatics and non-aromatics obtained from said extractive distillation columns at a point in proximity to the borderline between the extractive stripper section and the extractive rectifier section of each column system, outlet means at the top of said distillative rectifying section for the desired aromatics, conduit means for passing the extraction agent and non-aromatics from the bottom of 3 the extractive stripper section to the next column system and conduit means for feeding back the extraction agent from the last extractive stripper section to the first ext stt t st a
  • An extractive distillation apparatus comprising at least two extractive distillation columns arranged in series and having connected to the last extractive distillation column a plurality of column systems arranged in series, at least one of said column systems being comprised of an extractive rectifying section superposed on said extractive stripper section, and a distillative rectifying section and a distillative stripper section, the last two sections being superposed on each other, means connecting the top of said extraction rectifying section and a point in proximity to the boundary between said two distillative sections, outlet means at the top of said distillative rectifying sections for the desired aromatics, conduit means for passing the extraction agent and non-aromatics from the bottom of the extractive stripper section to the next column system, and conduit means for feeding back the extraction agent from the last extractive stripper section to the first extractive distillation column.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Analytical Chemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
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US674682A 1966-10-13 1967-10-11 Simplified extractive distillation process for obtaining aromatics of differing boiling-point ranges Expired - Lifetime US3554873A (en)

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US (1) US3554873A (de)
JP (1) JPS4832514B1 (de)
AT (1) AT276352B (de)
BE (1) BE704416A (de)
ES (1) ES345842A1 (de)
GB (1) GB1142543A (de)
NL (1) NL153512B (de)
SE (1) SE357957B (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4115206A (en) * 1977-07-21 1978-09-19 Phillips Petroleum Company Separation of phenol-, cyclohexanone-, and cyclohexylbenzene-containing mixtures employing an organic carbonate
US4401515A (en) * 1980-03-15 1983-08-30 Japan Synthetic Rubber Co., Ltd. Process for producing 1,3-butadiene or 2-methyl-1,3-butadiene having high purity
US5180474A (en) * 1991-03-23 1993-01-19 Krupp Koppers Gmbh Method of separation of aromates by extractive distillation

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4115206A (en) * 1977-07-21 1978-09-19 Phillips Petroleum Company Separation of phenol-, cyclohexanone-, and cyclohexylbenzene-containing mixtures employing an organic carbonate
US4401515A (en) * 1980-03-15 1983-08-30 Japan Synthetic Rubber Co., Ltd. Process for producing 1,3-butadiene or 2-methyl-1,3-butadiene having high purity
US5180474A (en) * 1991-03-23 1993-01-19 Krupp Koppers Gmbh Method of separation of aromates by extractive distillation

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JPS4832514B1 (de) 1973-10-06
BE704416A (de) 1968-02-01
GB1142543A (en) 1969-02-12
NL153512B (nl) 1977-06-15
DE1568931A1 (de) 1970-03-26
SE357957B (de) 1973-07-16
NL6713947A (de) 1968-04-16
AT276352B (de) 1969-11-25
ES345842A1 (es) 1968-11-16

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